I was out riding this morning on a 100k charity ride, and got behind these two younger fitter-looking guys. We came to a little hill after a while, and both proceced to pedal out of the saddle going up the hill, and I managed to downshift and pass them. "That pedaling-out-of-the-saddle isn't as effective as they thought", I thought to myself. After a while they passed me again, and then at the next little hill, the episode was repeated. I guess it was the third time they passed me, it finally dawned on me they were both riding fixed gear bikes. Doh!